Known polyalkylene ether glycols include polyethylene glycol, poly-1,2- and 1,3-propylene ether glycol, polytetramethylene ether glycol, polyhexamethylene ether glycol and copolymers thereof. They have been used widely as lubricants or as starting materials for preparing lubricants used in the molding of rubbers and in the treatment of fibers, ceramics and metals. They have also been used as starting materials for preparing cosmetics and medicines, as starting materials or additives for water-based paints, paper coatings, adhesives, cellophane, printing inks, abrasives and surfactants and as starting materials for preparing resins, such as alkyd resins. They have also been used as soft, flexible segments in the preparation of copolymers and segmented copolymers such as polyurethanes, thermoplastic polyesters and unsaturated polyester resins. Examples of commercially important polyether glycols include polyethylene glycol, poly(1,2-propylene glycol), ethylene oxide/propylene oxide copolyols, and polytetramethylene ether glycol.
Among the polyether glycols, the most widely used polyether glycol is poly(1,2-propylene glycol) (PPG) because of its low cost. This polymer is non-crystalline, liquid at room temperature and hence easy to handle. However, PPG has secondary hydroxyl end groups and it contains high percentages of terminal unsaturation.
Polyoxytrimethylene glycol or polytrimethylene ether glycol or poly(1,3-propylene glycol) can be derived either from 1,3-propanediol or from oxetane. These polytrimethylene ether glycols have primary hydroxyl groups and have low melting points and are highly flexible.
U.S. Pat. No. 2,520,733, which is incorporated herein by reference, discloses polymers and copolymers of trimethylene glycol and a process for the preparation of these polymers from trimethylene glycol in the presence of a dehydration catalyst such as iodine, inorganic acids (e.g., sulfuric acid) and organic acids. The trimethylene glycol derived polymers disclosed in this patent are dark brown or black in color. The color can be improved to a light yellow color by treatment processes disclosed therein. Polymers of molecular weight from about 100 to about 10,000 are mentioned; however, there is a preference for molecular weights of 200–1,500 and the highest molecular weight shown in the examples is 1096.
U.S. Pat. No. 3,326,985, which is incorporated herein by reference, discloses a process for forming a polytrimethylene glycol having an average molecular weight of 1,200–1,400. First, polytrimethylene glycol which has an average molecular weight of about 900 is formed using hydriodic acid. This is followed by an after treatment which comprises vacuum stripping the polyglycol at a temperature in the range of 220–240° C. and at a pressure of 1–8 mm Hg in a current of nitrogen from 1–6 hours. The product is stated to be useful in preparing polyurethane elastomers. There is also presented a comparative example directed to producing polytrimethylene glycol with a molecular weight of 1,500.
U.S. Pat. No. 5,403,912, which is incorporated herein by reference, disclosed a process for the polymerization of polyhydroxy compounds, including alkanediols having from 2–20 carbon atoms, in the presence of an acid resin catalyst at temperatures of from 130–220° C. Molecular weights of from 150 to 10,000 are mentioned. A copolymer of 1,10-decanediol and 1,3-propanediol having a number average molecular weight of 2050 was exemplified.
Preparation of ester terminated polyethers and hydroxy terminated polyethers from oxetanes and or mixtures of oxetanes and oxolanes by ring opening polymerization is disclosed U.S. Pat. No. 4,970,295, which is incorporated herein by reference. The resulting polyethers are stated to have molecular weights in the range of 250–10,000, preferably 500–4,000. Synthesis of polyoxytrimethylene glycols from oxetane is also described in S. V. Conjeevaram, et al., Journal of Polymer Science: Polymer Chemistry Ed., Vol. 23, pp 429–44 (1985), which is incorporated herein by reference.
It is desirable to prepare said polyether glycol from readily available materials, not, for example, from the commercially unavailable oxetane. The polytrimethylene ether glycols heretofore obtained from the polycondensation of 1,3-propanediol are of low molecular weight, are highly discolored and/or require long reaction times. In addition, heretofore all process for preparing polytrimethylene ether glycol from 1,3-propanediol reactant have been batch processes. Therefore, a continuous process that produces polytrimethylene ether glycol in high yield, preferably with little or no color, and desired molecular weight, has been sought.